Servo-actuating mechanism for pneumatic analog computers



May 2, 1967 D. w. CHAPIN ETAL 3,316,815

SERVO*ACTUATING MECHANISM'FOR PNEUMATIC ANALOG COMPUTERS Original Filed Dec. 4, 1961 4 Sheets-Sheet l IN V EN TORS S O DONALD W. CHAP/N By DONALD H. FISCHER am MK?, C@

ATTORNEY SERVO-ACTUATING MECHANISM FOR PNEUMATIC ANALOG COMPUTERS 4 Sheets-Sheet 2 Original Filed Dec. 4. 1961 ill! www. 0/ l! 1MM Ih mg l I l Il l Il um w a l n.. MM 00 DD I I ll L V. B m 2. w a@ 6 M H May 2, 1967 D. w. cHAP|N ETAL 3,315,815

SERVO-ACTUATING MECHANISM FOR PNEUMATIC ANALOG COMPUTERS 4 Sheets-Sheet 5 Original Filed Dec.

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'Arron/vn May 2, 1967 D. W. CHAPIN ETAL SERVOACTUATING MECHANISM FOR PNEUMATIC ANALOG COMPUTERS Original Filed Dec. 4, 1961 INPUT DIAPHRAGM AREA INPUT 4 Sheets-Sheet 4 Posmve FEEDBAcK AREA ouTPuT SPRING MAss PlsToNARl-:A posmo" AND sENslNG AND A ELEMENT P SPRING RAT mVENroRs gon/41.0 u'. CHAP/N? FEEDBACK A By o/vALD H. F/scHE sPRaN@ A TTORNEY United States Patent C 3,316,815 SERVO-ACTUATING MECHANISM FOR PNEUMATIC ANALOG COMPUTERS Donald W. Chapin, Scottsdale, and Donald H. Fischer,

Phoenix, Ariz., assignors to TheGarrett Corporation, Los Angeles, Calif., a corporation of California Original application Dec. 4, 1961, Ser. No. 156,810, now Patent No. 3,239,139. Divided and this application June 24, 1965, Ser. No. 466,670

6 Claims. (Cl. 91-359) This -application is a division of application Ser. No. 156,810 filed Dec. 4, 19611, now Patent No. 3,239,139, by Donald W. Chapin et al., for Pneumatic Analog Computer.

The invention forming the subject matter of this application relates generally to analog computeres of the type to which the application mentioned above is directed, but is more particularly concerned with an vactuator employed in and forming part of such computers.

Still more particularly, this invention relates to a servoactuator used to adjust the position of an element, which forms a part of an analog computer, in response to variable pressure signals transmitted to the computer from the system under the control thereof.

An object of this invention is to provide a servo-actuator which is responsive to pressure signals to adjust a force applying element of a computer relative to a beam or other movable element, the servo-actuator having aV fluid pressure operated member and valve means for controlling the application of fluid pressure thereto together with means for transmitting feedback forces from such member to the valve means.

Another object of the invention is to provide a servoactuator of the type mentioned in the preceding paragraph having means associated therewith for sensing a predetermined condition of the servo-actuator `and controlling the application of iiuid pressure in accordance with the condition as it is sensed.

Still another object of the invention is to provide a servo-actuator for adjusting an element of an analog computer in accordance with a signal transmitted from a system being controlled by such computer, the actuator being provided with a control mechanism responsive to the signal and to the operation of the actuator so that a precise positioning of the computer element will be secured.

A further object of the invention is to provide a servoactuator for use in an analog computer, the actuator having a double-acting iluid pressure operated piston and a novel mechanism for controlling the application of Huid pressure to the piston, such mechanism being responsive to a signal from a system under control of the computer and to a signal fed back to the mechanism from the piston whereby accurate location of a part of the computer in accordance with the selected system signal will result.

A still further object of the invention is to provide a servo-actuator for an analog computer having a doubleacting fluid pressure operated piston and a mechanism for controlling the application of fluid pressure to the piston, the control mechanism having an element biased in oneV direction by a iirst resilient means to apply fluid pressure to such piston to elfect movement thereof in a first predetermined direction, such element being moved by a second resilient means, rendered effective by movement of the piston in said rst direction to a position to apply il'uid pressure to the piston to move it in the opposite direction, the first resilient means being controlled by means responsive to a signal from a source extraneous of the analog computer.

The above and other features and objects of the inven- ICC tion will be apparent from the following detailed description and the accompanying drawings, in which:

FIG. l is a schematic view, partly in section, of a pneumatic analog computer of the type shown in the application referred to previously, to which a servo-actuator embodying the principles of the present invention has been applied;

FIG. 2 is a plan view of a part of the computer shown in FIG. 1;

FIG. 3 is a vertical sectional view of the portion of the computer shown in FIG. 2 on the plane indicated by the line III-III of FIG. 2;

FIG. 4 is an enlarged vertical sectional view taken through the control mechanism for the servo-actuator forming a part of the analog computer shown in FIG. 1;

FIG. 5 is an enlarged sectional view taken through a valve means, forming a part of the control mechanism, on the plane indicated by the line V--V of FIG. 4;

FIG. 6 is a front elevational view of a spring element employed in the actuator control mechanism, the View being taken on the plane indicated by the line VI-VI of FIG. 4; and

FIG. 7 is a block diagram of various force applications in the operation of the servo-actuator forming the subject matter of the invention.

While the invention forming the subject matter of this application relates only to a servo-actuator, the pneumatic analog computer to which the actuator is particularly applicable and in connection with which it has been illustrated will be generally described to facilitate a better understanding of the invention.

`Referring now to the drawings, and particularly FIG. 1, a flexible pneumatic analog computer unit 20 embodying the present invention comprises a lever box or supporting frame 21 having a force balancing lever 22 mounted therein for limited rotation about a centrally disposed stationary fulcrum 23. Forces may be applied to either or both the top and bottom sides 24 and 25, re spectively, of the lever 22 and on either or both sides of the stationary fulcrum 23 by means of a plurality of force or pressure applying carts 26. In FIG. 1, two of the carts 26, designated as B and D, are arranged for applying forces against the upper side 24 of the lever 22 on each side of the fulcrum 23. Said carts are adjustably or movably mounted on upper tracks 27 suitably mounted or secured in the vertical side walls or members of the rectangular frame 21. Similarly, two carts 26, designated A and C, are arranged for applying forces against the lower or bottom side 25 of the lever 22 on each side of the fulcrum 23. These carts are adjustably positioned on lower tracks 28 which are parallel to the tracks 27 and also mounted in the side walls of the frame 21.

Depending upon the particular type of calculation or function to be performed by the computer unit 20, said unit may also include a servo-actuator 30 forming the subject matter of the present invention for positioning one or more of the carts 26 in response to a predetermined input pressure to the servo. When it is desired to perform diierenentiation or integration with the computer, some means of providing resistance and capacitance (RC) is also required, and this is accomplished in the present instance by the component 31 shown in FIG. 1. Thus, the `ilexible computer unit comprises a plurality of components: (l) a lever box 21, including a supporting frame, and a lever having a stationary fulcrum and a sensing element; (2) a plurality of carts 26 for applying forces which are sensed by the sensing element so that the lever may be balanced; (3) a servo-actuator 30 for automatically moving one or more carts during and as part of a computation; and (4) a combination resistance and capacitance 31. Since the servo-actuator constitutes the instant Patented May 2, 1967V 3 invention, the following detailed description will be directed primarily thereto.

Each of the carts 26 consists of a main body portion or carriage 44 having longitudinal openings therein lined with suitable bushings for the reception of the track members 27 or 28. Each carriage 44 is split or notched at 45 in line with the longitudinal openings for the tracks, so that said carriage may be squeezed into firm locked contact with the tracks by a locking screw 45A. A piston or pressure chamber housing 46 is attached to the carriage 44 and positioned so that a force applying roller or wheel 47 may bear `against either the top or bottom surface of the lever 22 and act to eliminate friction as the card is moved.

The servo-actuator The servo-actuator 30 is a device which positions a piston and its load (in this case, one or more of the carts 26) in response to an input pressure. Referring to FIGS. 1 and 4, it will be observed that the servo-actuator, which is mounted on the end wall 32 of the lever box, comprises a forward, output, or piston housing portion 86 and a rearward or input housing portion lS7, which are cylindrical in shape and interconnected by suitable uid pressure conduits which will be described below. The piston or output housing 86 -has an inner cylindrical chamber 8S in which a movable wall 90 inthe form of a cylindrical piston is disposed for movement. This piston is sealed from the inner wall of the housing with a double diaphragm 91 and is provided with an elongated, hollow, axial shaft portion 92 which is suitably sealed from an inwardly projecting neck 93 by a `diaphragm 94. Piston 90 divides the inner chamber 88 into first and second output chambers 95 and 96, so that a pressure differential between them will cause the piston to move in the housing. Such movement may be transmitted to one of the force applying carts 26 by a connecting rod 97, threaded at one end into a special 'fitting 9S mounted in the outer end of the hollow shaft 92 and secured at its other end to the cart housing by :a set screw 100.

Special rfitting `98 has an inner threaded portion 101 to adjustably receive one end of an elongated tension feedback spring 102 which has its other end straightened into a rod portion 103. By turning the spring on the threaded portion 101, both the length and spring rate of the spring may be adjusted. As best shown in FIGS. 4 and 6, rod 1'03 is provided with a lug 104 for contact with the center of a double cantilever spring 105, having its peripheral portions in contact with the end wall of the chamber 95. lRod 103 then passes through an opening in the housing 87, which is sealed with a bushing 106, and into a vertically disposed cylindrical passage 107. At that point the end of rod 103 is connected to a rod or knife edge mem* ber 108 mounted on the end of a shaft 109 connected to a pressure responsive piston 110. Shaft 109 and piston 110 are arranged and sealed :in a suitably shaped axial chamber 111 with a forward shaft sealing diaphragm 112 and a rearward piston sealing diaphragm 113. The space between these diaphragms forms a pressure chamber 114. Another double cantilever spring 115 is in operative contact with the rearward end of piston 110 through a screw 116. The assembly, consisting of the rod 103, piston 110, and associated parts, is thus resiliently centered and held in place in the housing 87 by a pair of double cantilever springs 105 and 115, having the same advantages and features of operation. The end of housing section 87 may be closed with a cover member 116A having an opening therein so as to subject the outside of piston 110 and diaphragm 113 to ambient pressure. This is different from the construction shown in FIG. 1, which will be more fully described hereinafter.

It will be apparent that the force on the piston 110 created by the pressure differential betwen that in chamber 114, which is subjeced to input pressure through a passage 117, and ambient, will be balanced against the force in feedback spring 102 created by the position of piston 90. Such balance is sensed by a sensing device 118 shown in FIGS. 4 and 5 having outlet ports 77 thereof connected to the chambers 95 and 96, by lines 95 and 96', respectively. Like parts are designated with like names and lreference numerals, both in the drawing and the following description. As shown in FIGS. 4 and 5, the valve portion of the sensing device 118 includes a sleeve 73 supported in the housing portion 87, the sleeve having inlet ports and grooves and 81 communicating with a source of fluid pressure via passages Ps. The sleeve provides a valve bore 74 for reception of ball valves 76 which are movable to control communication between ports 77 and either the atmosphere through port l85 or the fluid pressure source through ports 80. As mentioned, ports 77 communicate via groove 78 and lines 95', 96' with the piston chamber sections 95 and 96. Precise setting of ball valves relative to ports 77 is accomplished throngh adjustment of screw 71 into or out of actuating finger 70. In FIG. 4, the bifurcated actuating finger 70 is mounted on the end of a cantilever rod 119 housed in chamber 107 and spring mounted and biased to the left by a leaf spring 120. This spring is suitably connected to the cantilever rod 119 at one end and fixed in a plug 121 tted into and closing the lower end of the chamber 107. An aperture 122 is provided in the yrod 119 and sized so that the rod 103 may extend through it and allow the rod 108 to seat on the rearward edge thereof as illustrated.

When the ball valves 76 precisely register with ports 77, as shown in FIG. 5, no appreciable flow to or from the chambers V95 and 96 can take place and piston 90 will be held stationary. If, however, finger 70 is moved by rod 119 under the influence of pressure signals applied to chamber 114, valves 76 will be moved to admit pressure to one of the chambers 95, V96 and to connect the other with the atmosphere. As a result, piston of the servoactuator will move, causing similar movement of the cart 26 connected therewith. As previously indicated, movement of piston 90 causes the transmission of a feedback signal via spring 102 and associated mechanism to the rod 119 and other parts of the control.

There are several features of the servo-actuator, as just described, which make it highly sensitive and render its operation more laccurate than other servomechanisms that have been available in the past. Some of these features are illustrated in the block diagram of FIG. 7, where it will be noted that the input consists of the force on piston shaft 109 resulting from the application of the input pressure against the diaphragm stack 112, 113 (FIG. 4). This force is counteracted by the force from feedback tension spring 102, the amount of force depending upon the degree of contraction or extension of the spring 102. If these two forces are not in balance, the sensing lever 119 is caused to move and thereby move the sensing element 118. The fluid connections are such that the output pressure acts upon the piston 90 and moves it sufficiently to balance the feedback force with the input.

According to the present invention, there are additional important features in the construction of the servo-actuator. There is, for example, the effect of the movement of the sensing leve-V119 which is mechanically transmitted directly back to the output; and there is also an inner loop through which a positive feedback is applied to increase the forward gain of the servo-actuator force system. This is accomplished by the pressure differential between the piston chamber and ambient pressure over an effective area equal to the cross section of the rod 103. It Will be apparent that as pressure increases in chamber 95 all surfaces exposed to the inside of the chamber will be subjected to the force of such pressure. Since rod 103 extends through the end wall of the Ihousing 86 and has its cross-sectional area exposed to ambient pressure (through member 108, shaft 109 and piston 110), the force of the 5 pressure in the chamber will be effective over such area (projected through the lug 104 to the right-hand end surface thereof and to the rightwardly facing surface of the straight portion of spring 102 extending to the right from lug 104) and transmitted through rod 103 to member 108, permitting lever 119 to be moved toward the left by spring 120 or other forces acting in such direction. This feedback force pushes toward the rod 108 in a position between the input and output and adds to the total gain and sensitivity of the device.

The schematic arrangement shown in FIG. l was devised to provide a flexible demonstration unit with which all of the mathematical functions can be performed merely by changing pressure connections. It differs from the more detailed construction of FIGS. 2-7, in several important respects which account for its flexibility. For example, the chamber 130 to the left of the piston 110 is connected by a conduit 131 with a pressure manifold 132 having a plurality of pressure lines connected thereto under control of suitable valves 133. The inlet ports of the servo-sensor 118 are also connected t-o the supply pressure. The RC 31 has pressure lines P0 and P0' connected to corresponding lines in the manifolds 132. Finally, for ease of manipulation, carts A and B are interconnected by a tie rod 136.

Each of the carts A, B, C, and D has its pressure line connected to a manifold 132, as indicated. All of the manifolds may be connected to any suitable source of fluid pressure when the FIG. l apparatus is to be demonstrated and the input pressures P1, P2, and P3, etc., are derived from this source by means of suitable regulators (not shown). The output pressures Pg and P are then determined by the particular mathematical function for which the FIG. 1 apparatus is set to perform. The demonstration apparatus of FIG. l is specifically designed and set up for the process industry standard pressure range of 3-15 p.s.i. The supply pressure Ps is preferably above this operating range, at 30 p.s.i., for example, to insure effective operation of the sensing device 118. The constant pressure Pc is set at 3 p.s.i.; the pressure is set at the level about which integration or differentiation is to take place. The set pressure is only applied to the servodiaphragms to cause the servo to be fully extended at the outset of the operations in which the servo is used. As mentioned above, the pressures P1, P2, and P3 are the variable pressures, which are selected and set (within the operating range) by the'demonstrator or operator to illustrate the examples; and the output pressures P0 and P0 are the result of the particular mathematical function being performed.

Where the servo is used in the computation, carts A and B will be positioned by said servo; and in those functions where the servo is not used, it is adjusted or set to position the carts A and B in about the positions shown in FIG. 1.

It will be readily understood by those skilled `in the art that various changes may be made in the construction of the servo-actuator for use in a pneumatic analog computer and certain features thereof may be employed without others without departing from the invention or sacrificing any of its advantages.

We claim:

1. A servoactuator for adjusting the position of a force applying cart in a pneumatic analog computer, comprising:

(a) a housing having a piston chamber in one end thereof and a sensing means adjacent to said piston chamber;

(b) a piston arranged for movement in said chamber and having a shaft extending outside said housing for connection With said force applying cart;

(c) means associated with and responsive to the operation of said sensing means for applying fluid pressure to said piston;

(d) an actuating member operatively connected to said sensing means and having limited movement in two directions;

(e) a feedback spring operatively connected to said piston and actuating member, movement of said piston tending to cause said feedback spring and actuating member to interrupt the application of fluid pressure to said piston; and

(f) means disposed in part in said pistou chamber and responsive to the application of fluid pressure to said piston to apply a force directly to said feedback spring to modify the feedback action thereof.

2. A servo-actuator for adjusting the position of a force applying cart in a pneumatic analog computer, cornprising:

(a) a housing having a piston chamber in one end thereof and a sensing means adjacent to said piston chamber;

(b) a piston arranged for movement in said chamber and having a shaft extending outside said housing for connection with said force applying cart;

(c) means associated with and responsive to the operation of said sensing means for applying fluid pressure to opposite sides of said piston;

(d) an actuating member operatively connected to said sensing means and having limited movement in two directions;

(e) a feedback spring operatively connected to said piston and actuating member, movement of said piston tending to cause said feedback spring and actuating member to interrupt the application of fluid pressure to said piston;

(f) pneumatically actuated means for moving said actuating member in the second direction; and

(g) positive feedback rrieans disposed in part in said piston chamber and formed with said feedback spring and responsive to the application of fluid pressure to said piston for increasing the forward gain of said servo-actuator.

3. Servo-actuating means for adjusting the position of force applying means in a pneumatic analog computer, comprising:

(a) housing means forming a piston chamber and a sensor chamber adjacent thereto;

(b) piston means disposed for movement in said piston chamber, said piston means being provided with means for transmitting motion from said piston means to force applying means of the computer;

(c) control means in said sensor chamber, said control means having an actuator finger supported at one end for rocking movement and engaged at the other end with valve means for controlling the application of fluid pressure to said piston, said control means being responsive to movement of said piston means in a first direction to interrupt the application of fluid pressure to said piston means;

(d) fluid pressure responsive means for actuating said control means to cause it to apply fluid pressure to said piston means to move it in said first direction; and

(e) means responsive to fluid pressure applied to said piston means to move it in said first direction to apply a predetermined force to said actuator finger to move it in the same direction as said first-mentioned fluid pressure responsive means.

4. Servo-actuating means for adjusting the position of force applying means in a pneumatic analog computer,

comprising:

(a) housing means forming a main piston chamber,

a sensor chamber and a secondary piston chamber;

(b) a main piston means disposed for movement in said main piston chamber, said main piston means being provided with means for transmitting motion thereof to the force applying means of the computer;

and exposed to fluid pressure when said main piston j is exposed to the forward moving force to partially oppose the transmission of motion to said control means; and

(e) a secondary piston in said secondary piston chamber, said secondary piston being operatively connected with said control means and responsive to uid pressure to cause said control means to apply fluid pressure to said main piston to move it in the forward direction.

5. Servo-actuating means for adjusting the position of force applying means in a pneumatic analog computer, comprising:

(a) housing means forming a piston chamber and a sensor chamber adjacent thereto;

(b) piston means disposed for movement in said piston chamber, said piston means being provided with means for transmitting motion from said piston means to force applying means of the computer;

(c) control means in said sensor chamber, said control means having means providing a valve chamber with inlet ports at opposite ends and spaced outlet ports between the inlet ports, said outlet ports communicating with said main piston chamber at opposite ends thereof, the space between said outlet ports communicating with the ambient atmosphere;

(d) a pair of ball valve elements in said valve chamber for controlling communication of said outlet ports with said inlet ports and the ambient atmosphere;

(e) an actuating rod mounted in said sensor chamber and having a portion disposed between said ball valve elements for movement to place said ball valve elements in position to apply fluid pressure to said main piston to move it in opposite directions;

(f) feedback means for transmitting motion from said main piston to said actuating rod in a direction to move said ball valve elements to a position to interrupt the application `of fluid pressure to said main piston, said feedback means having a portion eX- posed to uid pressure used to move said main piston in one direction to partially oppose the transmission of motion to said actuating rod; and

(g) means in said secondary piston chamber responsive to fluid pressure to move said actuating rod in the valve actuating directions.

6. Servo-actuating means for adjusting the position of force applying means in a pneumatic analog computer, comprising:

(a) housing means forming a piston chamber and a sensor chamber adjacent thereto;

(b) piston means disposed for movement in said piston chamber, said piston means being provided with means for transmitting motion from said piston means to force applying means of the computer;

(c) control means in said sensor chamber, said control means having means providing a valve chamber with inlet ports at opposite ends and spaced outlet ports between the inlet ports, said outlet ports communicating with said main piston chamber at opposite ends thereof, the space between said outlet ports communicating with the ambient atmosphere;

(d) a pair of ball valve elements in said valve chamber for controlling communication of said outlet ports with said inlet ports and the ambient atmosphere;

(e) an actuating rod mounted in said sensor chamber and having a portion disposed between said ball valve elements for movement to place said ball valve elements in position to apply uid pressure to said main piston to move it in opposite directions;

(f) means for moving said actuating rod for effecting the operation of said ball valve elements having a secondary piston in said secondary piston chamber and a motion transmitting connection with said actuating rod, said secondary piston being responsive to fluid pressure to move said actuating rod and place said ball valve elements in position to apply uid pressure to said main piston to cause forward movement thereof; and

(g) feedback means establishing a yieldable motion transmitting connection between said main piston and said actuating rod, forward movement of said main piston tending to move said valve elements toward a position to interrupt the application of fluid pressure to said main piston said feedback means having a portion exposed to the Huid pressure employed to cause forward movement of said main piston to modify the operation of said feedback means.

References Cited by the Examiner UNITED STATES PATENTS 2,265,106 12/1941 FieuX 91-387 2,966,891 1/1961 Williams 91--387 2,967,544 1/ 1961 Pearsall.

2,995,116 8/1-961 Dobbins 137--86 3,003,475 10/1961 Rouvalis 91-387 3,222,995 12/ 1965 Reed 91--359 FOREIGN PATENTS 1,320,167 1/1962 France.

MARTIN P. SCHWADRON, Primary Examiner. 

1. A SERVO-ACTUATOR FOR ADJUSTING THE POSITION OF A FORCE APPLYING CART IN A PNEUMATIC ANALOG COMPUTER, COMPRISING: (A) A HOUSING HAVING A PISTON CHAMBER IN ONE END THEREOF AND A SENSING MEANS ADJACENT TO SAID PISTON CHAMBER; (B) A PISTON ARRANGED FOR MOVEMENT IN SAID CHAMBER AND HAVING A SHAFT EXTENDING OUTSIDE SAID HOUSING FOR CONNECTION WITH SAID FORCE APPLYING CART; (C) MEANS ASSOCIATED WITH AND RESPONSIVE TO THE OPERATION OF SAID SENSING MEANS FOR APPLYING FLUID PRESSURE TO SAID PISTON; (D) AN ACTUATING MEMBER OPERATIVELY CONNECTED TO SAID SENSING MEANS AND HAVING LIMITED MOVEMENT IN TWO DIRECTIONS; (E) A FEEDBACK SPRING OPERATIVELY CONNECTED TO SAID PISTON AND ACTUATING MEMBER, MOVEMENT OF SAID PISTON TENDING TO CAUSE SAID FEEDBACK SPRING AND ACTUATING MEMBER TO INTERRUPT THE APPLICATION OF FLUID PRESSURE TO SAID PISTON; AND (F) MEANS DISPOSED IN PART IN SAID PISTON CHAMBER AND RESPONSIVE TO THE APPLICATION OF FLUID PRESSURE TO SAID PISTON TO APPLY A FORCE DIRECTLY TO SAID FEEDBACK SPRING TO MODIFY THE FEEDBACK ACTION THEREOF. 